62 research outputs found
Vortex lattice studies in CeCoIn5 with H perpendicular to c
We present small angle neutron scattering studies of the vortex lattice (VL)
in CeCoIn5 with magnetic fields applied parallel (H) to the antinodal [100] and
nodal [110] directions. For H || [100], a single VL orientation is observed,
while a 90 degree reorientation transition is found for H || [110]. For both
field orientations and VL configurations we find a distorted hexagonal VL with
an anisotropy, Gamma = 2.0 +/- 0.05. The VL form factor shows strong Pauli
paramagnetic effects similar to what have previously been reported for H ||
[001]. At high fields, above which the upper critical field (Hc2) becomes a
first-order transition, an increased disordering of the VL is observed.Comment: 5 pages, 4 figure
Vortex lattice structure in BaFe2(As0.67P0.33)2 by the small-angle neutron scattering technique
We have observed a magnetic vortex lattice (VL) in BaFe2(As_{0.67}P_{0.33})2
(BFAP) single crystals by small-angle neutron scattering (SANS). With the field
along the c-axis, a nearly isotropic hexagonal VL was formed in the field range
from 1 to 16 T, which is a record for this technique in the pnictides, and no
symmetry changes in the VL were observed. The temperature-dependence of the VL
signal was measured and confirms the presence of (non d-wave) nodes in the
superconducting gap structure for measurements at 5 T and below. The nodal
effects were suppressed at high fields. At low fields, a VL reorientation
transition was observed between 1 T and 3 T, with the VL orientation changing
by 45{\deg}. Below 1 T, the VL structure was strongly affected by pinning and
the diffraction pattern had a fourfold symmetry. We suggest that this (and
possibly also the VL reorientation) is due to pinning to defects aligned with
the crystal structure, rather than being intrinsic.Comment: 9 pages, 9 figure
The pairing state in KFe2As2 studied by measurements of the magnetic vortex lattice
Understanding the mechanism and symmetry of electron pairing in iron-based
superconductors represents an important challenge in condensed matter physics
[1-3]. The observation of magnetic flux lines - "vortices" - in a
superconductor can contribute to this issue, because the spatial variation of
magnetic field reflects the pairing. Unlike many other iron pnictides, our
KFe2As2 crystals have very weak vortex pinning, allowing
small-angle-neutron-scattering (SANS) observations of the intrinsic vortex
lattice (VL). We observe nearly isotropic hexagonal packing of vortices,
without VL-symmetry transitions up to high fields along the fourfold c-axis of
the crystals, indicating rather small anisotropy of the superconducting
properties around this axis. This rules out gap nodes parallel to the c-axis,
and thus d-wave and also anisotropic s-wave pairing [2, 3]. The strong
temperature-dependence of the intensity down to T<<Tc indicates either widely
different full gaps on different Fermi surface sheets, or nodal lines
perpendicular to the axis.Comment: 13 pages, 3 figure
Observations of Pauli Paramagnetic Effects on the Flux Line Lattice in CeCoIn5
From small-angle neutron scattering studies of the flux line lattice (FLL) in
CeCoIn5, with magnetic field applied parallel to the crystal c-axis, we obtain
the field- and temperature-dependence of the FLL form factor, which is a
measure of the spatial variation of the field in the mixed state. We extend our
earlier work [A.D. Bianchi et al. 2008 Science 319, 177] to temperatures up to
1250 mK. Over the entire temperature range, paramagnetism in the flux line
cores results in an increase of the form factor with field. Near H_c2 the form
factor decreases again, and our results indicate that this fall-off extends
outside the proposed FFLO region. Instead, we attribute the decrease to a
paramagnetic suppression of Cooper pairing. At higher temperatures, a gradual
crossover towards more conventional mixed state behavior is observed.Comment: Submitted to New Journal of Physics, 13 pages, 4 figure
Antiferromagnetic ordering in a 90 K copper oxide superconductor
Using elastic neutron scattering, we evidence a commensurate
antiferromagnetic Cu(2) order (AF) in the superconducting (SC) high-
cuprate (y=0.013, =93 K). As
in the Co-free system, the spin excitation spectrum is dominated by a magnetic
resonance peak at 41 meV but with a reduced spectral weight. The substitution
of Co thus leads to a state where AF and SC cohabit showing that the CuO
plane is a highly antiferromagnetically polarizable medium even for a sample
where T remains optimum.Comment: 3 figure
In situ uniaxial pressure cell for x-ray and neutron scattering experiments
We present an in situ uniaxial pressure device optimized for small angle x-ray and neutron scattering experiments at low-temperatures and high magnetic fields. A stepper motor generates force, which is transmitted to the sample via a rod with an integrated transducer that continuously monitors the force. The device has been designed to generate forces up to 200 N in both compressive and tensile configurations, and a feedback control allows operating the system in a continuous-pressure mode as the temperature is changed. The uniaxial pressure device can be used for various instruments and multiple cryostats through simple and exchangeable adapters. It is compatible with multiple sample holders, which can be easily changed depending on the sample properties and the desired experiment and allow rapid sample changes
In situ uniaxial pressure cell for x-ray and neutron scattering experiments
We present an in situ uniaxial pressure device optimized for small angle x-ray and neutron scattering experiments at low-temperatures and high magnetic fields. A stepper motor generates force, which is transmitted to the sample via a rod with an integrated transducer that continuously monitors the force. The device has been designed to generate forces up to 200 N in both compressive and tensile configurations, and a feedback control allows operating the system in a continuous-pressure mode as the temperature is changed. The uniaxial pressure device can be used for various instruments and multiple cryostats through simple and exchangeable adapters. It is compatible with multiple sample holders, which can be easily changed depending on the sample properties and the desired experiment and allow rapid sample changes
Local structure study about Co in YBa(CuCo)O thin films using polarized XAFS
We have studied the local structure around Co in
YBa(CuCo)O thin films with three different
concentrations: x=0.07, 0.10, 0.17, and in a
PrBa(CuCo)O thin film of concentration x=0.05
using the X-ray Absorption Fine Structure (XAFS) technique. Data were collected
at the Co -edge with polarizations both parallel and perpendicular to the
film surface. We find that the oxygen neighbors are well ordered and shortened
in comparison with YBCO Cu-O values to 1.80 \AA{} and 1.87 \AA{} in the
-axis and -plane, respectively. A comparison of further neighbors in the
thin film and powder data show that these peaks in the film are suppressed in
amplitude relative to the powder samples, which suggests there is more disorder
and/or distortions of the Co environment present in the thin films.Comment: 14 pages; To be submitted to Phys. Rev.
High Pressure Effects on Superconductivity
The review is devoted to a discussion of the effects of high pressure imposed
on superconducting materials. Low-temperature superconductors, high-temperature
superconducting cuprates, and some unconventional superconducting compounds are
investigated. Experimental as well as theoretical results regarding the
pressure effects on Tc and other interesting properties are summarized.Comment: To be published in: "Frontiers in Superconducting Materials", Edt. A.
Narlikar, Springer Verla
NEUTRON SCATTERING TECHNIQUES APPLIED TO MARTENSITIC TRANSFORMATIONS AND SHAPE MEMORY ALLOYS
The advantages of thermal neutron scattering in materials science are shortly reviewed. Recent results obtained on the shape memory alloys Cu-Zn-Al and
Cu-Zn are presented and discussed. Emphasis is given to new, 'non-standard' techniques for the determination of effects of stacking faults on peak positions and intensities, short-range order and static displacements through elastic diffuse scattering, and temperature and concentration dependence of phonon dispersions close to the martensitic phase transition
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